1. Field of the Invention
The present invention relates to a ceramic-metal composite body, and more specifically the invention relates to a turbine rotor and a method of producing the same.
2. Related Art Statement
Since ceramics such as zirconia, silicon nitride and silicon carbide are excellent in mechanical strength, heat resistance and wear resistance, they have attracted attention as high temperature structural materials and wear resistive materials for gas turbine engine parts, engine parts and so on. However, the ceramics are inferior to the metallic materials in terms of shape formability because they are hard and brittle. Further, ceramics have weak resistance against impact forces due to their poor toughness. For this reason, it is difficult to form mechanical parts such as the engine parts only from the ceramic materials, and they are generally used in a composite structural body in which a metallic member is bonded to a ceramic member.
Heretofore, turbine rotors have been known as metal-ceramic composite bodies of this kind. FIG. 6 is a partial sectional view showing an example of such a turbine rotor. In FIG. 6, the turbine rotor is integrally formed by fitting a ceramic shaft 52 integrally formed with a turbine vane wheel 51 made of ceramics into a depression 54 of a metallic member 53. The fitting is ordinarily carried out through press fitting, shrink fitting, or expansion fitting. A fitting shaft 55 for mounting a compressor wheel not shown is provided on an opposite side to the turbine vane wheel side of the metallic member 53.
3. Problems to be solved by the Present Invention
The above-mentioned turbine rotor has been heretofore used in the state that the whole metallic member 53 had the same high hardness or only a part of the outer periphery of the depression-provided portion which was to be brought into contact with a bearing was further hardened. Therefore, the shaft 55 for fitting a compressor wheel had a high hardness.
In actual use, when a compressor wheel 57 fitted to the compressor wheel-fitting shaft portion 55 by means of a thrust bearing 58 and a tightening nut 56 as shown in FIG. 7 is rotated at a high speed, the compressor wheel 57 is elongated in an arrow direction in this figure, that is, outwardly in a radial direction. Consequently, a distance L of the compressor wheel 57 in this figure shortens. Thus, it has been necessary that the fitting shaft 55 was elastically elongated by means of the tightening nut 56 by a shortened amount of the distance L when the compressor wheel 57 was assembled. However, when the hardness of the compressor wheel-fitting shaft 55 is high as in the conventional case, the fitting shaft 55 cannot allow a necessary amount of the elastic deformation. Thus, there exists a defect that the shrink amount cannot be absorbed, and the compressor wheel 57 slackens during use.